feat(stdlib): Tiled P4 — objects, custom props/types, templates, opt-in spawn (#72)

- Object layers: all shapes (rectangle/ellipse/point/polygon/polyline/text) and
  custom properties parse and are queryable — Tiled.object_count / Tiled.object /
  Tiled.object_shape, and Tiled.prop / prop_int / prop_type over any object /
  tile / layer / map.
- Custom types: Tiled.load_types reads an objecttypes.xml project custom-type
  table so a class property resolves its default; enum values resolve as strings.
- Templates: Tiled.template reads a .tx/.tj, and Tiled.load merges each object's
  `template` reference under the instance's overrides (field inheritance).
- Opt-in spawning: Tiled.spawn / Tiled.spawn_layer map an object's class +
  properties onto Ludic components through the reflection ABI (Position from x/y,
  each property to a like-named field). Off by default — no gameplay coupling in
  the core load. Split into tiled_spawn.ludic, spliced only for a Tiled *game*
  (the world table exists only under has_ecs), so a plain map-reading tool never
  links against the reflection ABI.

Proven by library/tiled_p4.ludic (18 assertions) incl. the design's named
orthogonal-outside.tmx object shapes. x test: 95 passed.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/language/tiled/tiled-template.md

@@ -0,0 +1,14 @@
+---
+id: tiled-template
+name: Tiled.template
+category: tiled
+kind: namespace-method
+tokens: Tiled.template
+sig: Tiled.template(path: string) -> value
+tip: Read a template file into an object value.
+order: 27
+ns: Tiled
+member: template
+---
+
+Reads a <code>.tx</code>/<code>.tj</code> template file and returns its object <a href="value"><code>Value</code></a> — the reusable object definition an instance inherits. <a href="tiled-load"><code>Tiled.load</code></a> resolves each object's <code>template</code> reference automatically, merging the template's fields under the instance's overrides.